1. Field of the Invention
The present invention relates to a multi-layer wiring substrate having a laminate portion in which insulating layers and conductor layers are stacked alternately, and more particularly to a wiring substrate suitable for transmission of high-frequency signals.
2. Description of Related Art
Conventionally, a wiring substrate which includes a substrate core and laminate portions provided on opposite sides of the substrate core and each including insulating layers and conductor layers stacked alternately has been widely used as a package on which a semiconductor chip or the like is mounted. In a process of manufacturing a wiring substrate having such a structure, conductor layers formed of metal such as copper and insulating layers formed of resin must be stacked such that a sufficient degree of adhesion is ensured between them. If a sufficient degree of adhesion is not secured between each conductor layer and the corresponding insulating layer adjacent thereto, for example, heating at the time of re-flow may cause defects such as partial bulging or separation at the interface between each conductor layer and the corresponding insulating layer adjacent thereto. In order to prevent occurrence of such a defect, conventionally, there have been proposed various methods for treating the surfaces of conductor layers which adhere to corresponding insulating layers in order to enhance adhesion reliability (see, for example, Patent Document 1). In general, in the case where a conductor layer has a solid conductor portion to be connected to a power supply voltage or a ground potential, the problem of poor adhesion reliability becomes remarkable. An effective measure for enhancing adhesion reliability is performing a roughening treatment on the surface of the conductor layer. That is, when the surface of the conductor layer is roughened through etching or the like, fine protrusions and recesses are formed on the surface, whereby an anchor effect is attained. Thus, the reliability of adhesion between the conductor layer and the corresponding insulating layer can be enhanced.